Two-way relationship exists between daytime naps and dementia in elderly: Study

Older adults with increased napping habits during the daytimes suffer from higher risks of Alzheimer's dementia while the patients with Alzheimer's disease exhibit high frequency and duration of daytime napping. This reciprocal relationship between impaired cognitive function and sleep-wake disturbances was studied on 1401 participants of the Rush Memory and Aging Project.

Daytime napping among older people is a normal part of aging – but it may also foreshadow Alzheimer's disease and other dementias. And once dementia or its usual precursor, mild cognitive impairment, are diagnosed, the frequency and/or duration of napping accelerates rapidly, according to a new study.

The participants of the study, whose average age was 81 and of whom approximately three-quarters were female, wore a watch-like device that tracked mobility. Each prolonged period of non-activity from 9 a.m. to 7 p.m. was interpreted as a nap.

The device was worn every year continuously for up to 14 days, and once a year each participant underwent a battery of neuropsychological tests to evaluate cognition. At the start of the study, 75.7% of participants had no cognitive impairment, while 19.5% had mild cognitive impairment and 4.1% had Alzheimer's disease.

For participants who did not develop cognitive impairment, daily daytime napping increased by an average of 11 minutes per year. The rate of increase doubled after a diagnosis of mild cognitive impairment to a total of 24 minutes and nearly tripled to a total of 68 minutes after a diagnosis of Alzheimer's disease.

When the researchers looked at the 24% of participants who had normal cognition at the start of the study but developed Alzheimer's six years later and compared them with those whose cognition remained stable, they found differences in napping habits. Participants who napped more than an hour a day had a 40% higher risk of developing Alzheimer's than those who napped less than an hour a day; and participants who napped at least once a day had a 40% higher risk of developing Alzheimer's than those who napped less than once a day.

The research confirms the results of a 2019 study, of which Yue Leng was the first author, that found older men who napped two hours a day had higher odds of developing cognitive impairment than those who napped less than 30 minutes a day. The current study builds on these findings by evaluating both daytime napping and cognition each year, hence addressing directionality, Leng notes.

The study shows for the first time that napping and Alzheimer's disease "seem to be driving each other's changes in a bi-directional way," said Leng, who is also affiliated with the USCF Weill Institute for Neurosciences. "I don't think we have enough evidence to draw conclusions about a causal relationship, that it's the napping itself that caused cognitive aging, but excessive daytime napping might be a signal of accelerated aging or cognitive aging process," she said.

"It would be very interesting for future studies to explore whether intervention of naps may help slow down age-related cognitive decline.

To read the full articles click here:

Alzheimer's and Dementia: The Journal of the Alzheimer's Association.

2019 study